Critical Dimension Enhancement

of DUV Photolithography on the

ASML 5500/300

Francesca Calderon

Miramonte High School

August 13th, 20151

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g-line - 436 nm

i-line - 365 nm

DUV - 248 nm

DUV - 193 nm

resolution ~ 𝝀/2NA

[1] Krassenstein, Brian. "The Moore’s Law of 3D Printing… Yes It Does Exist, And Could Have Staggering Implications."

3DPrintcom. N.p., 28 June 2014. Web. 12 Aug. 2015.

Photolithography Review

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Bottom Anti Reflective

Coating - svgcoat3

Photoresist Coat - svgcoat6

DUV Exposure - asml300

Develop in MF26 - svgdev6

UV stabilize - axcelis/uv

bake

[2] "Semiconductor Lithography." The Basics of Microlithography. N.p., 23 Nov. 2006. Web. 03 Aug. 2015.

Background and History

➢It is understood that the current resolution limit

of the asml300 is 250 nm

➢The past baseline CMOS runs have successfully

made transistors with 350 nm features

➢Similar systems in other labs have been shown

to go down to 200 nm for an isolated line

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Background: Optical Column in Stepper

5[3] Ito, Takashi, and Shinji Okazaki. Nature. N.p., 31 Aug. 2000. Web. 12 Aug. 2015.

Theory: Annular Illumination

6[3] Ito, Takashi, and Shinji Okazaki. Nature. N.p., 31 Aug. 2000. Web. 12 Aug. 2015.

Goals➢Characterize properties of UV210-0.3, a new

photoresist○ generate a process specification for lab members to

reference

➢Determine the minimum feature size that can be

produced on the asml300○ Focus-exposure matrices and inspection with leo SEM

➢Characterize off-axis illumination and variable

numerical aperture○ Bossung and exposure latitude plots

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Tools Qualified On :

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axcelis

svgcoat3

svgcoat/dev6

asml300uvbake

Tools Qualified On :

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leoasiq

primeoven

nanospec

matrix

Experimental Method - Photoresist Characterization

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1. Coated wafers at different spin speeds

and measured film thickness

○ generate spin speed curve

2. Decided upon a spin speed to achieve

a targeted film thickness

3. Created a process specification to

define the final process

4. Ran process wafers to populate the

process specification

Experimental Results - Photoresist Characterization

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The vendor data sheet provided a spin speed curve that

closely matched our experimental results on svgcoat6

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Experimental Results - Process Specification

Experimental Method - Critical Dimension Enhancement

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1. Ran focus-exposure matrices

2. Measured linewidth with the leo SEM

3. Created Bossung and exposure latitude

plots

4. Determined ideal imaging conditions to

resolve 150 nm isolated lines

5. Patterned whole wafers with ideal

conditions to make sure the results were

repeatable

Intro to Bossung Plots

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What is important:

1. A change in exposure dose results in the smallest possible change in linewidth - ΔY

2. A change in focus results in the smallest possible change in linewidth - slope

Intro to Exposure Latitude Plots

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What is important:

1. A change in focus dose results in the smallest possible change in linewidth - ΔY

2. A change in exposure results in the smallest possible change in linewidth - slope

Experimental Results - Conventional Imaging

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Dose: 13 mJ/cm2

Focus: -0.23 um

Enhancement: none

Exposure Latitude: 186 nm - 117 nm = 69 nm

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

um

um

um

um

um

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Experimental Results - Critical Dimension Enhancement

Dose: 16 mJ/cm2

Focus: -0.23 um

Enhancement: NA = 0.6 Outer = 0.855 Inner = 0.550

Exposure Latitude: 151.5 nm - 142 nm = 9.5 nm

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

um

um

um

um

um

um

um

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Dose: 16 mJ/cm2

Focus: -0.23 um

Enhancement: NA = 0.6 Outer = 0.755 Inner = 0.450

Exposure Latitude: 161 nm - 157.5 nm = 3.5 nm

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

mJ/cm2

um

um

um

um

um

um

um

um

Experimental Results - Critical Dimension Enhancement

Chosen Image Settings

Exposure: 16 mJ/cm2

Focus: -0.23 microns

Numerical Aperture: 0.6

Annular Condition 1: Sigma Inner: 0.550

Sigma Outer: 0.855

Annular Condition 2: Sigma Inner: 0.450

Sigma Outer 0.75519

Experimental Results : Wafer Scale Performance, CD = 150 nm

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21 locations per wafer were measured

Best case imaging was observed with the small annular ring. It produced an average line

width of 150.3 nm, with a 90.5% yield.

Experimental Results : UV210-0.3 Cross-sectional Profiles

21Imaging conditions: 16 mJ/cm2, -0.23 um, NA=0.6 Sigma Outer=0.855 Sigma Inner=0.55

line width =

152 nm

sidewall angle

= 90º

aspect ratio ~ 2.5:1

Conclusion

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➢ 150 nm lines have been resolved in 3800 Å

thick UV210-0.3 photoresist

➢ The results found are consistent from wafer-to-

wafer and uniform across a wafer

➢ CD fidelity has good accuracy with the average

line width less than 1 nm from target and a

standard deviation approximately 11 nm

Acknowledgements - Thank You!

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★Jeff Clarkson

★Kim Chan

★Irving Garduno

★Greg Mullins

★David Lo

★Cheryl Chang

★Marilyn Kushner

★Bill Flounders

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